In 1944, Helen Duncan (1898-1956), a Scottish medium, was the last person to be convicted under the 1735 Witchcraft Act. A court was told she claimed to have conjured up the spirit of a sailor killed on HMS Barham during World War II. The sinking of this ship was supposed to be a military secret and the British authorities decided to prosecute because they reportedly feared that Helen Duncan might reveal plans for the D- Day landings. She was convicted of "pretending to raise spirits from the dead" and sentenced to 9 months in prison. The 1735 Witchcraft Act was finally repealed in 1951. -- Niki Pollock, University of Glasgow Library
You can read more about the Helen Duncan story here. Also, if you follow the University of Glasgow link above, you will find a fascinating and horrifying account of a 1591 witch trial.